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Last Updated: Thursday, 21 July 2005, 09:02 GMT 10:02 UK
Discovery given new launch date
Bill Parsons (AP)
Parsons: The best route is to go for a countdown
The US space agency has set Tuesday at 1039 EDT (1539 BST) as its new launch opportunity for the shuttle Discovery.

Nasa engineers have still not fixed the troublesome fuel sensor that stopped an earlier launch attempt but feel they are now getting on top of the issue.

Agency officials said they would start the countdown clock on Saturday for what will be the first shuttle mission since the loss of Columbia in 2003.

Discovery's 12-day venture into orbit will take it to the space station."

We have a great amount of work to do to get us through this but we all agree that this work is doable to take us to a launch on the 26th (of July)," shuttle programme manager Bill Parsons told reporters.

Controlled stop

At issue is the performance a low-level fuel cut-off sensor, which failed to give a correct reading during a routine pre-launch check last week.

Shuttle schematic (BBC)
Mission known as STS-114
Discovery's 31st flight
17th orbiter flight to ISS
Payload: Raffaello Multi-Purpose Logistics Module
Lift-off: 1039 EDT, 26 July
Location: Kennedy Space Center, Launch Pad 39B
Discovery crew: Collins, Kelly, Noguchi, Robinson, Thomas, Lawrence and Camarda

The sensor is one of four that warn the shuttle computers if the external tank is about to run dry.

This allows the computers to shut down Discovery's three main engines and its fuel pumps in an orderly fashion - neither too soon nor too late; both scenarios have potentially disastrous consequences.

Exhaustive work by hundreds of engineers suggests that an electrical grounding problem lurking somewhere inside the spacecraft is the most probable cause of the sensor's faulty behaviour.

Shuttle officials said some further tests still needed to be done but that they felt confident now to proceed to a countdown.

Clear plan

If the sensor worked properly during the final hours before launch, Discovery would fly, Bill Parsons said.

If the problem reoccurred but was well understood, then the go-ahead would likely be given to launch the orbiter anyway, he added.

Nasa workers (AP)
Nasa engineers will continue to work through the sensor problem
"We believe the best way to go through this is to do a countdown," he said. "If the sensors work exactly like we think they will, then we'll launch on that day.

"If anything goes not per the plan that we've laid out in front of us, then we'll have a scrub and we'll have to talk about it."

Including the first launch attempt on Tuesday, there are at least four opportunities for Discovery to launch during the current launch window, which extends until 31 July; although Nasa managers are now also looking at the possibility of additional launch opportunities in the first week of August.

It would be a controversial move to fly Discovery with a low-level fuel sensor still malfunctioning.

Nasa used to permit launches with only three of the four sensors working properly but then insisted on a four-out-of-four approach after the 1986 Challenger explosion.

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